Pyrometer circuit



March 29, 1960 K` J. KNuDsEN PYROMETER CIRCUIT Filed July 3. 1957 2Sheets-Sheet 1 w rmMN Rw md o .QQN N E u W n 1K ahw J .d m ,K l n s m\%N wm.; W

.a u a, m, N l, W wm NT Q NQ Q @A ww ww um mm |f,\N\ UQNN United StatesPatent .fPYRoMETER CIRCUIT d d l Knud J. Knudsen, Middlebury, Conn.,assiguor to Lewis ,Engineering Company, Naugatuck, Conn., a corpora tionof Connecticut `Application July 3, 1957, Serial vN0.-669,842 17 Claims.(Cl. 73-360) This invention relates to hightemperature thermometers orpyrometers employing thermocouples and potentiometer circuits having-slide wires.

One object of the -invention -is to -provide a novel and improvedpotentiometer-type `temperature indicator rwherein a very wide range ofvalues may be easilyand quickly covered by a simplified combination ofcontinuously -variable indicator means together with a step-typeindicator means. v

An additional object is to provide .an improved vpotentiometer circuithavingv a step-type indicator means, wherein the supply current isautomatically held at a constant, preset value vfor all positions of theindicator, thereby obviating the necessity for constant adjustment .andchecking of said current Aas different readings are taken. y

Another object of the invention is to provide va .fnovel fil 2,930,233Patented Mar. 29, 1950 ICC larcuate type, whereby the slider 12 thereofmay beconf nected to a rotaryknob and dial, shown respectively at 18 and19 in Fig. 2, for the purpose of providing convenient indications of theposition of the slider. As viewed vin Fig. 1, the left end of the slidewire 13 has .been labeled 100, and the right end has been labeled 0f; I

Included in the-thermocouple circuit are leads `20Qand 21 of Chromel andcopper respectively, Ajoined together at a cold junction 22, the copperlead '21 beingconnected with a contact arm 23 of deck #l of arnultipledeck selector switch indicated lgenerally by the numeral 25.Deck #l of the switch 25 comprises ya set of contacts l numberedrespectively 26 through 37, such contacts bepotentiometer-type`pyrometer circuit as above, wherein improved accuracy is had intemperature indications over a wide range of values, asgiven by a`selector-switch -or step-type indicator -means in conjunction with-acontinuously variable slide wire control.

Still another object of the invention is Ato vprovide an improvedpyrometer potentiometer circuit asabovefcharacterized, wherein apotentiometer vdrop resistor and slide-wire shunt resistor areincorporated and connected in a novel control circuit having a `switchorstep-,type indicator means, to the end thatV there may be effectedquick and easy temperature readings while maintaining high accuracythroughout the entire range-of operation. A further object of theinvention is to provide, fora potentiometer-type pyrometer having acold-junction compensating bridge, improved energizing circuits andchecking means therefor, wherein the necessary checking of thethermocouple and cold junction may be easily and quickly elfected, tominimize errors in the readings.

Other features and advantages will hereinafter appear. In the drawingsaccompanying this specificatiomsimilar characters of vreference indicatecorresponding parts wherever possible in the several views, in-which:

Figure l is a schematic circuit diagram of thetimprovedpotentiometer-type pyrometer with selector-switch and slide-wireindicators as provided by the invention. Fig. 2 is a front or face viewof the instrument panel of the pyrometer. p

Fig. 3 isa chart of connections effected by-an indicating selectorswitch of the ypyrometer circuit.

Referring rst to Fig. 1, the improved pyrometer shown therein comprisesa potentiometer-type circuit which may kbe adjustedand correlated withtemperatures of a thermocouple so as to provide, for example, tempera.ture readings, saidcircuit having ar usual .type of oppo sitelydeectablefinstrument .rnovementv10,j such;` asf-aygalvanometer ortDArsonval t movement one terminal of whichisconnectedfbyfa wire-11to,aslider,12 oft a-slide wirel13, ttheiotherlterminal of themovement 10 being connectetl. in. a` tl'lermocoupletr circuit: having,binding p0stS-15 andl'for connection to the thermocouple leads. As

ing engageable selectively one after `the other'by the contact arm 23.The set of contacts 26-37 is associated with .a drop-resistor meansindicated generally 4by thernurner-al 39, one end of which is connectedto that end of the .slide wire 13 which is labeled 0. The drop resistor39`has a plurality of different points which Vare connected tothe:switch contacts 26-37, and `such drop kresistor may be advantageouslyconstituted of a `plurality ofk individual resistors, 11` in number,connected respectively between different pairs of the contacts 26-37, asshown.

The contacts 26T-37 .have also been labeled, infl'jig l, ystarting with0 andterminating with 1100, suclide'signations being in 100 steps. l

The contact arm 23 of the selector switch 25 may have a knob 40 and`dial 4'1, A.see Fig. 2, by which the .positions of the arm `areindicated, and su'chy dial may be provided about its Aperiphery withrthesame temperature Vdesignations given above to the contacts 26-37v,to wit0, 100, 200, etc.

The thermocouple circuit vof-.the pyrometer furtherincludes a:compensating ybridge 43 of a type which vis known in the art, forpurposes of cold junction corn- Ypensation. The'bridge 43 may have legs44, 45, 46an`cl -47 connected in a diamond, the legs 45 `and -46 Abeingconnectedtoan Alumel wire y49 joined to the binding post 15 and the legs44 and .47 `being connected to 'a copper wire y50 rjoined totheremaininglterminal ofthe instrument :movement 10. .As shown, thebridge legs 45 and 47 may be ofjhigh temperature coefiicient `wire suchas copperornickel, or acombination of iboth.

In Vaccordance with1the present invention, inlconjuno tion withthe slide`wirel I` provide a novel Ayrton-type resistive shunt,and'circuit-andswitching .means including diiferent-valued seriesresistors associated therewith, for cooperation with thecontact arm 23and deck #1 of the selector switch 25 to effect a simplification in the,f

obtaining of temperature readings. IncludedV in thisvorganization is Aasecond contact deck, labeled deck-#2 of the switch 25, comprisinga setof contacts numbered 52-63respectively,rand a contact arm 64 `coupledltoand simultaneously movable with the contact armv23. @The contacts52-63 are Ypaired respectively with thecontacts.

26-37 so thatthe pairs are traversed one after another by the contactarms 23 and `64 in response to turning movement imparted to the knob 40shown'in Fig.2.

The Ayrton-type shunt comprises a resistor indicated generally by thenumeral 66, to'different pointsofiwhich the contacts 52-63 vareconnected in a unique manner and through series resistors the values ofwhich are sof" chosen as'to cause a constant load to be 'presented-atall times to theenergizingmeans forthe potentiometer.

circuit and thus a constanty load vcurrent when the-arms 23 and l64-traverse theswitchcontacts. "Ihissconst-itutes an important featureofrthe invention in.l .thatfibyrfapftm matically maintainingconstantsthe.energizingwcurrentlof the potentiometer circuit-.there isobviatedthe necessity forcontinual,,readjustrnentwherrmeasuringltemperatures, as will be more fully set forth below. The shunt resistor66 may be advantageously constituted of a plurality of individualresistors labeled 68-76 respectively, and the ends of the shunt resistor66 are shown as being con nected respectively to the ends of the slidewire 13.

By the present invention the contacts 52-63 are connected, through thesaid different values of series resistors, in both forward and reverseorders to points on the shunt resistor 66 constituted by junctionsbetween the individual resistors 63-75. Such order of connections hasbeen illustrated graphically in the chart of Fig. 3 and it may be notedfrom Fig. l that the contacts 52 and 54 are connected together by a wire78 and through a series resistor 79 to the junction between theresistors 70 and 71. The contacts 53 and 60 are connected together by awire 80 and through a series resistor 81 to the junction between `theresistors 71 and 72. The contacts 55 and 59 are connected together by awire 82 through a series resistor 33 to the junction between theresistors 69 and 70. Thel contacts S6, 57 and 58 are connected togetherby a wire 84 and through a series resistor 85 to the junction betweenthe resistors 68 and 69. The contact 61 is'connected by a wire 86through a series resistor 87 to the junction between the resistors 72and 73. The contact 62 is connected through a series resistor 88 to awire 89 joined to the junction between the resistors 73 and 74. And, thecontact 63 is connected by a Wire 90 through a series resistor 91 to thejunction between the resistors 74 Iand 75.

I have found that, by the above organization and with a suitableenergizing means for the potentiometer circuit it is possible, throughproper proportioning of the various resistors, to effect extremelyaccurate adjustment or correlation of the circuit with temperatures ofthe thermocouple, and accordingly accurate temperature indications usingthe dial 41 of the selector switch 25, when the slider 12 of the slidewire 13 is at either end of its travel, corresponding to the setting or100 setting as shown in Figs. l and 2. all without continualreadjustment of the supply current through the potentiometer circuit. Inother words, the total span or range of the slide wire reading,corresponding to the voltage drop across it, is adjusted by the actionof the contactor 64, thereby to provide accurate reading points at bothends of the slide wire, of temperatures throughout the range of fromzero to l200. Moreover, I have found that the remainder of the slidewire dial 19 may be uni-V formly marked olf in graduations of 10intervals and 1 intervals, as indicated, whereby readings ofconsiderable accuracy between the extreme positions of the dial 19 areobtainable, throughout the entire range of the selector switch 25 anddial 41 thereof. For example, an error less than 1 may be had throughoutthe entire range of movement of the dial 19 for any setting of theselector switch 25 and dial 41 thereof. It will be understood, ofcourse, that the slide wire 13 and slider 12 thereof are arranged toprovide infinitely variable readings between the various steps oftemperature indicated by the dial 41.

`As is usual with potentiometer circuits, the temperature indication maybe read when the dials 19 and 41 are adjusted to effect a null orzeroized indication at the instrument movement 10, such movement havinga usual type of dial and pointer, indicated at 92 in Fig. 2.

Through the provision of the series resistors 79, 8l, 83, 85, 87, 88 and91 a proper control of the load current may be effected for eachdifferent setting of the selector switch arms 23 and 64 whereby saidcurrent may be automatically held constant at a preset, checked valuethus making possible the obtaining of highly accurate temperaturereadings by manipulation of only the switch 25 and slider 12. In otherwords, regardless of the setting of the switch 25 the loading effectedby and the load current supplied to the potentiometer circuit willremain uniform, obviating the necessity of constant readjustment ofcurrent as the switch 2S is changed.

Thus, in accordance with my improved potentiometer circuit as above setforth, only two easily readable and .settable dials need be manipulated,in conjunction with the indicating instrument 10, 92 in order to obtainreadings of the above accuracy, providing that proper initialenergization of the potentiometer circuit is provided, and properenergization of the compensating bridge 43.

Given herewith is a table of representative variations or errors whichmay be expected at the midpoint of the slide wire dial 19 for varioussettings of the dial 41, when both ends of the slide wire dial readcorrectly.

Temperature setting In accordance with this invention I also providesepan rate battery energizing means respectively for the potentiometerand bridge circuits set forth above, Aand a novel and improvedorganization by which such energizing means may be readily checked andadjusted as to their values, thereby to maintain the accuracy of thetemperature indications given by the dials 19 and 41. Such checkingorganization further includes provision for maintaining a uniformloading of the batteries of the energizing means, thereby to minimizebattery voltage fluctuations. It is known that batteries upon beingdisconnected after a period of use will tend to be rejuvenated and havetheir voltage restored. Also, if during switching or other operations abattery is deprived of its load its voltage will rise and not againimmediately resume a steady discharge value. By the present invention Ieffect voltage stability in the batteries by maintaining the loadingthereof uniform.

Also, in the said organization I utilize but a single indicator devicefor making the said checks, together with a selecting switch mechanism,the latter being so arranged that the battery sources of thepotentiometer and bridge energizing means may be open-circuited when theinstrument is not in use, thereby to conserve battery life. Accordingly,referring to Fig. 1, the contact arm 64 of the switch 25 is connected bya wire 94 to a. battery 95` which is in turn connected by a wire 96 toan adjustable resistor' 97, the latter being advantageously in the formof a multiple-turn potentiometer-type of control device.

The potentiometer-circuit energizing means further comprises a wire 98connected to the switch contact 37, and such wire and the resistor 97are connected to a multiple pole selector switch indicated generally bythc numeral 100, said switch being shown as a tive pole threepositionswitch. The switch 100 has movable contacts or arms 101-105respectively, the contacts 101 and 102 being connected to a D.C.instrument movement 106 adapted for measuring current, through a seriesresistor 107. The instrument movement 106 may have a D.C. resistancevalue of 15 ohms, for example, and the resistor 107 may have a value of177 ohms, whereby the combined resistance is equal to 192 ohms. Theswitch contacts 103 and 104 are connected to a resistor 108 which has aresistance of 192 ohms, such resistor being termed a substitute resistorin that it is used alternatively with the indicator means comprising theinstrument 106, 107 so as to impose a continuous and uniform load on thebatteries of the energizing means, as will be shortly brought out.

The movable contact of the switch 100 is connected by a wire 110 to astationary contact 111 of the switch; which is engageable with thecontact 101 in switch posil *stationary 'contacts 1124115'respettivel'y,A fand b'tw'een -ntefcomaers-rli nu riz-fflcsnnec'r(arresten-r 1171s approriimatel-y' 1371 ohms. For switch position#3ithereiare provided "stationary contacts 119-1'2'3 respectively, the-zcontacts '1121' and 122 beingconnected respectively toethc Vcontacts`v'11,2 and 111. Also, fthe"contacts T1-19"=an"d'12t) yare"connectedrespectively to the contacts -113Ln'd :114. The switch'contacts 115 1and123 areconnectedtog'ether V4'anttto''the'lwire98 of the-'potentiometerenergizing' means. "Awire'12`5 connects the contact 112 to thevariableresis- ;tor"`97. Thefstationary-contacts of thes'witch'1`00,'shown l sie initial fcfiibr'ana l'at 'the iti-struinen,whereupbntheIfor the olf position #jlfare'devoid 'of any'connections.

`vide anfadjustable resistor 135, 4for 'Calibrating purposes. i

Values of various components in the above circuit may "be as follows:'Thebattery 127 may havea'voltageof 1.5, with a capacity such that itmay readily deliver ma. l Thei'b'attery95 may have a voltageof from `1.3'to '1".5 ,30

with'a' capacity ofk1`2'ma. The variable resistor "control -97y may havel60 ohms resistance', and the' indicating'meter `106 may have a lrangeto 5 ma.

iReferrin'gtoiFig. 2,"the"selector switch '100 :may have aknob 137, andthe three p'os'itionsthereof, ol position, 4thermocouple' test" positionand cold junction position may'be as indicated on the panel 13S of theinstrument. The indicator'instrument 106"`may have a dial 140 providedwith a zero current indication 141`and a maximum current'or checkindication`142, the'latter corresponding toa current of 5 ma., forexample. The adjustable resistor'97'may1have aiknob 144 for controllingit,and

the adjustable resistor 132 may have a knob 145'for the Same purpose.

Operation ofthe energizing means and switch controlled checking meanstherefora's'above set forth, is as follows: When the switch 100 is intheoff position #1, the batteries 127 and'95 will be open-circuited, and noenergy will be drawn therefrom. When the switch 100 is set in position#2, for thermocouple test,the'indicator means A106, 107 will'beconnectedca'cross the resistor '117 and r 'fresis'torfl-Ss'is'ftlrerfeafter'leftuntouche. v Y l Y a When the a'bov "two checkshave beenrnad'e, the'fs'with '100 maybeileft in either Vits #Zefo'r#Sposition-"to'obtain temperature readings, and itwill beunderstoodVthatthe -properlener'gy'is being 4supplied to the compensating bridgeVA43 land the 'potentiometer Asystem,fduplicating the energy utilizedduring the initial vvcalibration vof lthe instrument vatthefactoryfandaccordingly the overall high accuracy of the instrument may bevmaintained regardlessof varia'- 'tions inthe potentials'of thebatteries 95aud 127.l For the .purpose of enabling'the'zero 'position-ofthe instrument -106 to be readily checkedwithout'removing the normalload from the 'battery 95, I interpose in'the 'Wire'150 connected vtothe switch contact 102 a'push-button l`switch 151 normally maintainingclosed v"the circuit throughthe instrument 106. I also'provide aresistor 152 connected Vto theswitch'contact 101 and also toa Contact153 of the'push-button switch 151.' Whenthe said pushbutton switch 'isactuated, the circuit through 'theinstru-A 'ment 106 will be opened,whereas th'e'circuit'betwee'n the,

Vswitch'contacts 101l and 102 will remain closed through v the resistor152, and such latter resistor is made tohav'e a value of 192 ohmsjtothereby effect uniformity in the loading of thebattery 95 duringthe zerocheck of the instrument 106 at such times that the push-buttonswitch 151is actuated. ,Y u

, It will be understood from the foregoing that I 'have provided a noveland improved potentiometer-type pyrorneter which vmay be easily andquickly operated to obtain temperature indications having an Aextremelyhigh l degree of accuracy, such pyrometer having cold junction theswitch contact 105 willengage the contact 115 to Y- complete the batterycircuitthrough the resistor 117 and therpotentiorneter system. Theresistor'97 is now adjusted to obtain a5 ma.,reading at the instrument106, designated .as the check indication in Fig. 2. By virtue of theshunt resistor 117, this may correspond actually'to a current of 1`2'ma."dr'awnfrom the battery 95. -While this vis oc curring, the resistor 108is maintaining closed Athe circuit through the battery 127, and isimposing a load thereon equivalent to that of the indicating means 106,107. Thus, the battery 127 in being accustomed to such load, will holdits voltage constant. Now, when the switch 100 is thrown to the #3position, the resistor 108 will he 'applied across the resistor 117 as asubstitute `for`thein dicator meansy 106, 107, and thelatter will benowsinserted inthe circuit with the battery 127. InV consequence ofthis,the'loa`ding of the battery 95 will-be maintained by the resistors108 and v117, and thesarne loading will be'applied tothe battery 127that itfhadfor position #2, Yknow inthe-'form of the iridicatormeans106, 107. .ihe adjustable control v132 is now 'varied to obtainmaximumdeflection 'of "the instrument' 106, 'corresponding to a orr-v Arent of"5 ina. `which is `being`supplied by the battery. 127, Preferably a highresistance settingis obtained v at the control J132'b`y suitablyadjusting the resistor 135, during compensation the accuracy of whichmay be ,maintained by repeated' checkin'gof the'ener'gizing means forthe compensating bridge. vThe samecheckingme'ans may be used forchecking vvthe lenergizatio'n ofl the potentiometer system, "and invconjunction "with I such checking `Ihavej provided 'novel .means forr'maintaining a uniform loading of "the 'separate batteries, thereby tominimize voltagev drift thereof. 'y Y Y y The pyrometer isseen to berelatively'sim'ple, small and compact, and tojoper'ate so as to provideaccurate'temperature indications over va'wide range ofivalues, all'inareliable manner and throughout an extended periodof use. i

' Variations and modifications may be made within the scope of theclaims, 'and portions of the improvements may be used without others.

I claim:l v Y v 1. In a potentiometer-type pyrometer circuit forconnection to a thermocouple, an oppositely 'deecting in strumentmovement; a series-connected islidewire and tapped voltage-dropresistor, one end of said resistor being connected to one end oftheslide wire; a two-lead therinocouple circuit and a 'slider for bsaidslide-wire, said slider 'and 'one lead off'said thermocouple circuitbeing connected respectively to 'terminals of said instrument movement;a selectorvswitch having a contact armiconnected tothe other lead ofs'aid .thermocouple circuit, said switch having a plurality of contactsconnected .to different taps of said drop resistor; an Ayrton-type shuntresistor connected 'across said slide wire; an energizing cir-V cuithaving one lead connected to the other end of said dropresistor; and asecond selector switch having acontact arm connected to the `other leadof said energizing circuit and having a plurality of contacts connectedIto points on said shunt resistor to cause a voltage drop 2. In apotentiometer-type pyrometer circuit 'for connection to a thermocouple,anoppositely Adetlecting instrument movement; a series-connected slidewire and tapped voltage-drop resistor, one end of said resistor beingconnected to one end of the slide wire; a two-lead thermocouple circuitand a slider for said slide wire, said slider and one lead of saidthermocouple circuit being connected respectively to terminals of saidinstrument movement; a selector switch having a contact arm connected tothe other lead of said thermocouple circuit, said switch having aplurality of contacts connected to'different taps of said drop resistor;an Ayrton-type shunt resistor connected across said slide wire; anenergizing circuit having one lead connected to the other end of saiddrop resistor; and a second selector switch having a contact armconnected to the other lead of said energizing circuit and having aplurality of contacts connected to points on said shunt resistor tocause a voltage drop across the slide wire, said switches being gangedto effect simultaneous movement of the contact Varms thereof whereby thevoltage drop across the slide wire is automatically regulated as theganged switches are actuated to correlate the circuit to a giventhermocouple temperature, thereby to maintain accuracy of saidcorrelation when the slider for the slide wire is at either end of thewire, the contacts of the first-mentioned selector switch beingconnected in regular order to progressive points on the drop resistor,and the contacts of the second selector switch being connected some inforward order and some in reverse order to progressive points on thesaid shunt resistor.

3. In a potentiometer-type pyrometer circuit for connection to athermocouple, an oppositely deiiecting instrument movement; aseries-connected slide wire and tapped voltage-drop resistor, one end ofsaid resistor being connected to one end of the slide wire; a two-leadthermocouple circuit and a slider for said slide wire, said slider andone lead of said thermocouple circuit being connected respectively toterminals of said instrument movement; a selector switch having acontact arm connected to the other lead of said thermocouple circuit,said switch having a plurality of contacts connected to different tapsof said drop resistor; an Ayrton-type shunt resistor connected acrosssaid slide wire; an energizing circuit having one lead connected to theother end of said drop resistor; and a second selector switch having acontact arm connected to the other lead of said energizing circuit andhaving a plurality of contacts connected to points on said shuntresistor to cause a voltage drop across the slide wire, said switchesbeing ganged to effect simultaneous movement of the contact arms thereofwhereby the voltage drop across the slide wire is automaticallyregulated as the ganged switches are actuated to correlate the circuitto a given thermocouple temperature, thereby to maintain accuracy ofsaid correlation when the slider for the slide wire is at either end ofthe wire, the contacts of the first-mentioned selector switch beingconnected in regular order to progressive points on the drop resistor,and the contacts of the second selector switch being connected some inforward order and some in reverse order to progressive points on thesaid shunt resistor, the contacts of the second selector switchconstituting a set traversable one after another by the contact arm froma beginning point to an end point, the initially and nally traversedcontacts being connected to points on the shunt resistor in a forwardorder, and intermediate contacts being connected to points on the shuntresistor in a reverse order.

4. In a potentiometer-type pyrometer circuit for connection to athermocouple, an oppositely deecting instrument movement; aseries-connected slide wire and tapped voltage-drop resistor, one end ofsaid resistor being connected to one end of the slide wire; a two-leadthermocouple circuit and a slider for said slideV Wire, said slider andone lead of said thermocouple circuit being fi i) connected respectivelyto terminals of said instrument movement; a selectorl switch having acontact arm Vconnected to the other lead of said thermocouple circuit,said switch having a plurality of contacts connected to different tapsof said drop resistor; an Ayrton-type shunt resistor connected acrosssaid slide wire; an energizing circuit having one lead connected to theother end of said drop resistor; and a second selector switch having acontact arm connected to the other lead of said energizing circuit andhaving a plurality of contacts connected to points on said shuntresistor to cause a voltage drop across the slide wire, said switchesbeing ganged to effect simultaneous movement of the contact arms thereofwhereby the voltage drop across the slide wire is automaticallyregulated as the ganged switches are actuated to correlate the circuitto a given thermocouple temperature, thereby to maintain accuracy ofsaid correlation when the slider for the slide wire is at either end ofthe wire, the contacts of the first-mentioned selector switch beingconnected in regular order to progressive points on the drop resistor,and the contacts of the second selector switch being connected some inforward order and some in reverse order to progressive points on thesaid shunt resistor, the contacts of the second selector switchconstituting a set traversable one after another by the contact arm froma beginning point to an end point, the initially and nally traversedcontacts being connected to points on the shunt resistor n a forwardorder, and intermediate contacts being connected to points on the shuntresistor in a reverse order, all of the contacts of said selectorswitches being paired for simultaneous and selective engagement by thesaid switch arms, and some of the contacts of the second selector switchbeing connected directly to other contacts thereof.

5. In a potentiometer-type pyrometer circuit for connection to athermocouple, an oppositely deecting instrument movement; aseries-connected slide wire and tapped voltage-drop resistor, one end ofsaid resistor being connected to one end of the slide wire; a two-leadthermocouple circuit and a slider for said slide wire, said slider andone lead of said thermocouple circuitbeing connected respectively toterminals of said instrument movement; a selector switch having aContact arm connected to the other lead of said thermocouple circuit,said switch having a plurality of contacts connected to diiferent tapsof said drop resistor; and Ayrtontype shunt resistor connected acrosssaid slide wire; an energizing circuit having one lead connected to theother end of said drop resistor; and a second selector switch having acon tact arm connected to the other lead of said energizing circuit andhaving a plurality of contacts connected to points on said shuntresistor to cause a voltage drop across the slide wire, said switchesbeing ganged to effect simultaneous movement of the contact arms thereofwhereby the voltage drop across the slide wire is automaticallyregulated as the ganged switches are actuated to correlate the circuitto a given thermocouple temperature, thereby to maintain accuracy ofsaid correlation when the slider for the slide wire is at either end ofthe wire, the contacts of the iirst-mentioned selector switch beingconnected in regular order to progressive points on the drop resistor,and the contacts of the second selector switch being connected some inforward order and some in reverse order to progressive points on thesaid shunt resistor, the contacts of the second selector switchconstituting a set traversable one after another by the contact arm froma beginning point to an end point, the initially and nally traversedcontacts being connected to points von the shunt resistor in a forwardorder, and intermediate contacts being connected to points on the shuntresistor in a reverse order, the contacts of the second selector switchexceeding nine in number, and the first and third contacts thereof beingconnected directly to each other. l

6. In a potentiometer-type pyrometer circuit for con- ,w Lr'iecticmros'athermocouple, 'ran oppositely:detiectingrinfstrument movement; fsaI=series.'c:onn`et:ted:igslide l-wireIzla-nd :tapped-,voltage-.dropresistor, .one end: of, said resistorbeing connected to one endo'f,the;`slide,wire;ratwoflead thermocouplecircuit anda slider for saidslidevwire, said slider ,androne lead of said thermoeouple circuitvbeing connected respectively .to terminals .f of ,said .instrumentmovement; aselector switch having a vcontactl arm connected tofthe other-lead of said thermocouple circuit, said switch having ya pluralityofcontacts connected to-diierent tapsof said :drop resistor; anAyrton-type shunt resistorconnected across said slide wire; anenergizing circuithavingone lead connected tothe other'l end ofsaidwdropfrresistor,and a second` selector'switch havinggacontact armconnected Vtothe other lead of said energizing circuit and havingavplurality-of contacts connected to points on.said shunt resistor tocause a voltage drop across the-.slide wire, said switches being gangedto eifect simultaneous movement of the contact arms thereof 'wherebyAthe voltage drop across the slide wire isV automatically regulated asthe ganged switches are actuated to correlateA the circuit to agiventhermocouple temperature,-thereby to'` maintain accuracy of saidcorrelation when the slider vfor the slide Awire is at either end of thewire, the contacts of the lfirstmentioned selector switch beingconnected in regular:

order to progressive points on the drop resistor, andthe contactsof thesecond selector switchfbeing connected some in forward order and some inreverse order to progressive points on the said shunt resistor, thecontacts of the second selector switch constituting a vset traversableone after another byA the contact armV from "a beginning point to an endpoint, the initially and finally traversed contacts being connected topointson the shunt :exceeding :.nine s in .fznurben the 'i first and:thirdlicontacts r Y .vbeingi connectedtidirectlyrto reachgother'gthesecoridzzancl ninth contactsrbeingfconnecteddirectlyV to each:l other,'Sand therfourth an'dffeighthxrcontacts ybeingv connected :directlytto'zeachfother. L n i hE8. Inra'potentiometeratype' pyrometer. circuitfor`con- -nection to av thermocouple, :an fwoppositely -deflectingzinstrument movement; "sa series-'connectedv slide wire andtappedvoltagedropresistor, one end of said resistorbeing connectedtozoneendf'offtheslide wire; a two-lead thermo-Acouplercircuit;andzazsliderfforv said slide wire, saidslider :andoneieadiofrsaid thermocouple circuit being. connectedrespectivelypto,termina'ls-'ofvsaid 'instrument movementga a selector"swith i having a "contact arm connected to the othersleadofsaidthermocouple circuit, said-switch havingaLpluralityofcontactsconnected to differcnt'taps of said dropV resistor;ian Ayrton-type'shunt resistor con- :.nected. acrossisaidy slidewire;.an energizing circuit having onelead connectedftozthe ,othery endof saiddrop resistor; and-1a second=selectoriswitch having 'a contactVarm connected *to the other leadv ofusaid energizingf circuit Tandhaving a plurality of 'contactsiconnectedto points'on said resistor in aforward orderand intermediate contactsf being connected to points on theshunt resistorr in areverse order, the contacts of thesecondselectorrswitch exceeding nine in number, the'frst and 'thirdcontacts thereof being connected directly to each other. and Vthe vsecond-,and ninth contacts thereof being connected di-v rectly to Veachother.

7. Ina potentiometer-type pyrometer circuit -tforconnection to athermocouple, an oppositely deecting instrument movement; aseries-connected slide wire and tapped kvoltage-drop resistor, one endof said resistor being connected to one end of the slide wire; atwo-lead thermocouple circuit and arslider for said slide wire, saidslider and one lead of said thermocouple circuit being connectedrespectively to terminals of said instrument movement;` a selectorswitch having a contact arm connected tothe other lead of saidthermocouple circuit, said switch having a plurality of contactsconnected to different taps of said drop resistor; an Ayrton-type shuntresistor connected across said slide-wire; an energizing circuit havingshuntfresistorto.:causei-a1voltage.drop across 'theslide -wire, saidswitches"being'zgangedto'effect simultaneous movement of thecontactarmsr thereof whereby the volt- Y -age'drop acrossthexslidelwireisr'automatically regulated as .the gangedwswitches are actuated toVcorrelate'the'cir- `cuit`=to ia given thermocoupletemperature, thereby"to, maintainlaccuracyf'ofsaidlcorrelation when the sliderjfor l `,theslide wire is: at either, end of the wire, the contactsiof the`first-mentioned selector switchbeing connectedin regular order toprogressive pointslon the `drop resistor, Yand the contactstofthe second`selector switch being connectedsome in,T forward order and some inreverse order .to progressvepointsfon the said shunt resistor, thecontactsof vthe secondselectorswitch constituting a set traversableoneafteran'othervby the contact arm fromfa beginning pointv to an endpoint, the initially and lfinally traversed contacts being connected topoints on` the shunt resistorxin a-forward order, andintermediatecontacts being connected to points onfthe shunt resistor inareverse'order, the contacts of the =second selector switch n exceedingninerin number, the first and thirdV contacts thereofbeingconnectedzdirectly to each other, the second l andninth contacts beingconnecteddirectly to each other,

one leadconnected tothe other-end of said drop fre# Y sistor; and asecond selector switchhaving a contact arm connected to the-other leadof-said energizing'circuit and havinga plurality of contacts connected`to points on said shunt resistor to cause avoltage drop -across theslide wire, said switches being ganged to'effect simultaneous movementof the contact arms thereof whereby the voltage drop across the slidewire is automatically regulated as the ganged switches are actuated tocorrelate the circuit to a given thermocouple temperature, thereby tomaintain accuracy of said correlation when the slider vfor the slidewire is at either end of the wire, the contacts of the first-mentionedselector switch being connected in regular order to progressive pointson the drop resistor, and the contacts of the second selector,switch-being connectedsome in forward order and some in reverseorder toprogressive,pointslonthe said shunt resistor, the contacts of thersecond ,selector switch constituting Ya .set traversable.one-afterfanother by the contactarm fromea beginning point' tocanendpoint, the initially andfnally traversed contacts. being, connectedto points vonthe shunt resistor in La forward order, f and intermediatekcontacts the fourthandeighthcontacts being Vconnectedvdirectlytozeach'other, andthe' fth,sixth and seventh contacts being connecteddirectly to each other.

9. Inta potentiometer-type lpyrometer circ'ui't-for'con-V nectionz'to athermocouple,an oppositelyfdeilecting instrument movement; aiSeries-connected slide wire and tapped voltage#drop resistor,ioneren'dof saidresistor being connected'to one end of'theslide wire; `a twolea'd'thermocouplefcircuitland'a sliderl for said slide wire, "saidsliderlandLonel'lead 'of'said thermocouple circuit'being connectedrespectively "to terminals `of said instrument movement;'a:selectorswitch having a contact arm fconnected'i-to'-theother vlead of saidthermocouple circuit, saidiswitch having-a plurality of contactsconnected `to different taps ofrsaid 'drop resistor; an Ayrton-typeshunt resistorzconnected v'across Isaid slide wire; an energizingcircuit havingtone lead connected to the otherl end of said dropresistor; =andfa secondselector switch having acontactarmconnectedto'the other leadl of said energizing circuit andrhavingva plurality-of contacts connected to points onrsaidshunt'resistorv to cause-a voltagedroplacross the slidewire,saidjswitches'beingganged toe'ffect simuli taneous movement 'ofi'the contact 1 arms thereof t whereby Y theivoltagertdropiacrossithevrs'lide wire is fautomaticlly 11 connected with the said shunt resistorand second switch, for maintaining a constant load on the energizingcircuit for different positionsfof the said ganged contact arms, therebyto effect a constant Vloadcurrent in said circuit.

10. In a potentiometer-type pyrometer circuit for connection to athermocouple, an oppositely deecting instrument movement; aseries-connected slide wire and tapped voltage-drop resistor, one end ofsaid resistor being connected to onev end of the slide wire; a two-leadthermocouple circuit and a slider for said slide wire, said slider andone lead of said thermocouple circuit being connected respectively toterminals of said instrument movement;'a selector switch having acontact arm connected to the other lead of said thermocouple circuit,said switch having a plurality of contacts connected to different tapsof said drop resistor; an Ayrton-type shunt resistor connected acrosssaid slide wire; an energizing circuit having one lead connected to theother end of said drop resistor; and a second selector switch having acontact arm connected to the other lead of said energizing circuit andhaving a plurality of contacts connected to points on said shuntresistor to cause a voltage drop across the slide wire, said switchesbeing ganged to effect simultaneous movement of the contact arms thereofwhereby the voltage drop across the slide wire is` automaticallyregulated as the ganged switches are actuated to correlate the circuitto a given thermocouple temperature, thereby to maintain accuracy ofsaid correlation when the slider for the slide wire is at either end ofthe wire, and resistors interposed between the said contacts of thesecond switch and the said shunt resistor, having values such that aconstant load is imposed on the energizing circuit for differentpositions of the said ganged contact arms, thereby to effect a constantload current.

11. In a potentiometer-type pyrometer circuit for connection to athermocouple, an oppositely detlecting instrument movement; aseries-connected slide wire and tapped voltage-drop resistor, one end ofsaid resistor being connected to `one end of the slide wire; a two-leadthermocouple circuit and a slider for said slide wire, said slider andone lead of said thermocouple circuit being connected respectively toterminals of said instrument movement; a selector switch having acontact arm connected to the other lead of said thermocouple circuit,said switch having a plurality of contacts connected to different tapsof said drop resistor; an Ayrton-type shunt resistor connected acrosssaid slide wire; an energizing circuit having one lead connected to theother end of said drop resistor; and a second selector switch having acontact arm connected to the other lead of said energizing circuit andhaving a plurality of contacts connected to points on said shuntresistor to cause a voltage drop across the slide wire, said switchesbeing ganged to elect simultaneous movement of the contact arms thereofwhereby the voltage drop across the slide wire is automaticallyregulated as the ganged switches are actuated to correlate the circuitto a given thermocouple temperature, thereby to maintain accuracy ofsaid correlation when the slider for the slide wire is at either end ofthe wire, all of the contacts of the said selector switches being pairedfor simultaneous and selective engagement by the said switch arms, andsome of the contacts of the second selector switch being connecteddirectly to other contacts thereof.

12. In a potentiometer-type pyrometer circuit for connection to athermocouple, an oppositely deecting instrument movement; aseries-connected slide wire and tapped voltage-drop resistor, one end ofsaid resistor being connected to one end of the slide wire; a two-leadthermocouple circuit and a slider for said slide wire, said slider andone lead of said thermocouple circuit being connected respectively toterminals of said instrument movement; a selector switch having acontact arm connected to the other lead of said thermocouplecircuit,said switch having. a plurality of contacts connected to diierent tapsof nected across said slide wire; an energizing circuit having one leadconnected to the other end of said drop resistor; and a second selectorswitch having a contact arm connected to the other lead of saidenergizing circuit and having a plurality of contacts connected topoints on said shunt resistor to cause a voltage drop across the slidewire, said switches being ganged to effect simultaneous movement of thecontact arms thereof whereby the voltage drop across the slide wire isautomatically regulated as the ganged switches are actuated to correlatethe circuit to a given thermocouple temperature, thereby to maintainaccuracy of said correlation when the slider for the slide wire is ateither'end of the wire, all of the contacts of said selector switchbeing paired for simultaneous selective engagement by the said switcharms, some of the contacts of the second selector switch being connecteddirectly to other contacts thereof; and series resistors disposed in theconnections to the taps on the said shunt resistor.

13. In a potentiometer-type pyrometer circuit for connection to athermocouple, an oppositely dellecting instrument movement; aseries-connected slide wire and tapped voltage-drop resistor, one end ofsaid resistor being connected to one end of the slide wire; a two-leadthermocouple circuit and a slider for said slide wire, said slider andone lead of said thermocouple circuit being connected respectively toterminals of said instrument movement; a compensating bridge in seriesin said thermocouple circuit; a pair of separate adjustable energizingcircuits connected one to input terminals of said bridge and the otherto the unjoined ends of said slide wire and drop resistor, saidenergizing circuits including batteries; an indicator means and asubstitute resistor having a resistance substantially equal to saidindicator means; and switching means for simultaneously inserting saidindicator means and substitute resistor respectively in series in saidenergizing circuits, and in alternation therein.

14. In a potentiometer-type pyrometer circuit for connection to athermocouple, an oppositely deecting instrument movement; aseries-connected slide wire and tapped voltage-drop resistor, one end ofsaid resistor being connected to one end of the slide wire; a two-leadthermocouple circuit and a slider for said slide wire, said slider andone lead of said thermocouple circuit being connected respectively toterminals of said instrument movement; a compensating bridge in seriesin said thermocouple circuit; a pair of separate adjustable energizingcircuits connected one to input terminals of said bridge and the otherto the unjoined ends of said slide wire and drop resistor, saidenergizing circuits including batteries; an indicator means and asubstitute resistor having a resistance substantially equal to saidindicator means; and switching means for simultaneously inserting saidindicator means and substitute resistor respectively in series in saidenergizing circuits, and in alternation therein, said indicator meansincluding a meter and a resistor connected in series; an additionalresistor and a manually operable switching means for optionallysubstituting said additional resistor for said meter and series resistorto enable a zero check of the meter to be had, said additional resistorhaving a resistance value equal to the combined resistance values of themeter and series resistor.

15. In a potentiometer-type pyrometer circuit for connection to athermocouple, an oppositely deecting instrument movement; aseries-connected slide wire and tapped voltage-drop resistor, one end ofsaid resistor being connected to one end of the slide wire; a two-leadthermocouple circuit and a slider for said slide wire, said slider andone lead of said thermocouple circuit being connected respectively toterminals of said instrument movement; a compensating bridge in seriesin said thermocouple circuit; a pair of separate adjustable energizingcircuits connected one to input terminals of said bridge and the otherto the unjoined ends of said slide wire and drop resistor, saidenergizing circuits including batteries; an indicator means and asubstitute resistor having a resistance substantially equal to saidindicator means; and switching means for simultaneously inserting saidindicator means and substitute resistor respectively in series in saidenergizing circuits, and in alternation therein, and a series resistorpermanently connected in the energizing circuit for the said slide wireand drop resistor, said switching means connecting either said indicatormeans or said substitute resistor across the said series resistor.

16. In a potentiometer-type pyrometer circuit for connection to athermocouple, an oppositely deflecting instrument movement; aseries-connected slide wire and tapped voltage-drop resistor, one end'ofsaid resistor being connected to one end of the slide wire; a two-leadthermocouple circuit and a slider for said slide wire, said slider andone lead of said thermocouple circuit being connected respectively toterminals of .said instrument movement; a compensating bridge in seriesin said thermocouple circuit; a pair of separate adjustable energizingcircuits connected one to input terminals of said bridge and the otherto the unjoined ends of said slide wire and drop resistor, saidenergizing circuits including batteries; an indicator means and asubstitute resistor having a resistance substantially equal to saidindicator means; and switching means for simultaneously inserting saidindicator means and substitute resistor respectively in series in saidenergizing circuits, and in alternation therein, and a series resitsorpermanently connected in the energizing circuit for the said slide wireand drop resistor, said switching means connecting either said indicatormeans or said substitute resistor across the said series resistor, saidindicator means comprising an instrument movement responsive to currentmoving through it and having a single indicating markvcorresponding to apredetermined value of current for which either of said energizingcircuits will be properly set to minimize error in the pyrometercircuit. f

Y 17. In a potentiometer-type pyrometer circuit for con- Y couplecircuit and a slider for said slide wire, said sliderV and one lead ofsaid thermocouple circuit being connected respectively to terminals ofsaid instrument movement; a compensating bridge in series in saidthermocouple circuit; a pair of separate adjustable energizing circuitsconnected one to input terminals of said bridge andthe other to theunjoined ends of said slide wire and drop resistor, said energizingcircuits including batteries; an indicator means and a substituteresistor having a resistance substantially equal to said indicatormeans; and switching means for simultaneously inserting said indicatormeans and substitute resistor respectively in series in said energizingcircuits, and in alternation therein, said switching means having an foiposition wherein the said batteries are both open-circuited.

References Cited in the file of this patent UNITED STATES PATENTS1,199,724 Wunsch Sept. 26, 1916 1,285,563 Cornman et al Nov. 19, 19181,912,242 Albert May 30, 1933 2,003,681 Doyle June 4, 1935 2,083,408Stein June 8, 1937 2,277,365 Michael Mar. 24, 1942 2,883,617 LathropApr. 2l, 1959

